This invention relates to projection exposure apparatuses and device fabrication methods using these apparatuses. Specifically, the present invention is suitably applicable to a projection exposure apparatus, e.g., of a step-and-repeat or a step-and-scan type, as a kind of fabrication apparatus used in a lithography process for devices such as semiconductor devices, which properly illuminates reticle and wafer surfaces to facilitate a high resolution.
The conventional process for fabricating semiconductor chips sequentially overlays and transfers minute patterns created on multiple masks onto a wafer surface.
This operation uses an illumination apparatus in an exposure apparatus to illuminate a mask (or reticle) arranged in a position optically conjugate with the wafer, so as to project and transfer a pattern on the mask onto the wafer surface via a projection lens.
The image quality of the pattern transferred onto the wafer is primarily dependent on the performance of the illumination apparatus, for example, the uniformity of its luminous intensity distribution on the mask and wafer. For example, Japanese Laid-Open Patent Application No. 10-270312 discloses the illumination apparatus that uses an inner-surface reflecting optical integrator (or a beam mixer) and a wave-front splitting optical integrator (or a multi-beam generating means) to improve the uniformity of the luminous intensity distribution.
FIG. 5 shows a partial schematic view of a projection exposure apparatus that uses an illumination apparatus which employs inner-surface reflecting and a wave-front splitting integrators.
FIG. 5 shows a step-and-repeat or step-and-scan projection exposure apparatus used for fabricating semiconductor chips such as LSIs and VLSIs, and devices such as CCDs, magnetic sensors, and liquid crystal devices.
In FIG. 5, 1 denotes a laser light source such as an ArF or KrF excimer laser. 2 denotes an incoherently turning optical system (a coherency decreasing means) that turns a coherent laser beam from the light source 1 into an incoherent one so that there may be no speckles on a plate 12. 3 denotes a beam shaping optical system for shaping a beam from the incoherently turning optical system 2 into a desired beam shape. 4 denotes an optical element for retaining an angle of exit, and for serving to maintain the angle of exit constant regardless of a status of an incident beam.
5 is a condensing optical system, which condenses beams from the optical element 4 and leads them to a plane of incidence 6a of the optical pipe 6 (or beam mixing means). The beam mixing means 6 uses beams from the condensing optical system 5 to create multiple virtual light sources (virtual images of the light source), and mix beams from multiple virtual light sources so as to make the luminous intensity distribution uniform on the plane of exit 6b. 
7 denotes a zoom optical system (or image-forming system). This optical system 7 projects beams from the beam mixing means 6 onto a plane of incidence 8a of a fly-eye lens as the multiple beams generating means 8 under various magnifications, and enables (a coherence factor) "sgr" to change continuously during zooming. At that time, the optical pipe 6""s plane of exit 6b and the fly-eye lens 8""s plane of incidence 8a are approximately conjugate with each other. In other words, the optical system 8 can form an image on the plane of exit 6b onto the plane of incidence 8a, and change the image size.
The fly-eye lens 8 forms multiple secondary light source images in the neighborhood of its plane of exit 8b. 
9 denotes an irradiating means including a condenser lens and the like, which condenses a beam from each element lens in the multiple beams generating means 8, and superimposes and uniformly illuminates a plane to be irradiated 10 as a plane forming a pattern on a mask or reticle (called a xe2x80x9creticlexe2x80x9d hereinafter).
11 is a projection optical system. The optical system 11 has a telecentric system at the side of its plane of exit, and demagnifies and projects the pattern on the reticle 10 onto the wafer (plate) 12.
FIG. 6(A) is a schematic view from the optical pipe 6 to the wafer 12 in the above conventional example described above, addressing "sgr" (or the size of an illumination beam within a plane of pupil) in the projection optical system 11, where the optical pipe 6 has a square cross section.
Optical pipe 6""s plane of exit 6b that includes the square cross section is transcribed to the fly-eye lens 8""s plane of incidence 8a in an approximately conjugate manner through a zoom optical system 7. Since the fly-eye lens 8 is an aggregate of element lenses, the light quantity distribution on the plane of incidence 8a is transmitted on an as-is basis to the plane of exit 8b. 
Therefore, for the square 6b in this case, 8b also has a square light quantity distribution.
Beams exiting from the fly-eye lens 8""s plane of exit 8b pass through the condenser lens 9 and Kohler-illuminates the reticle 10. The plane of exit 8b and projection optical system 11""s plane of pupil 11pupil are in an approximately conjugate relationship.
If a distribution of illumination light in projection optical system 11""s plane of pupil 11pupil is indicated as 11illum, the illumination light distribution 11illum also becomes a square distribution from the above relationship as shown in FIG. 6(B).
"sgr" represents the magnitude of the illumination light in projection optical system""s plane of pupil. However, in this case, a ratio between "sgr"0 in a direction of 0xc2x0 (or a vertical direction in the figure) and "sgr"45 in a direction of 45xc2x0 to the direction 0xc2x0 is a ratio between a side length and a diagonal length in a square, as can be understood from FIG. 6(B). Consequently, "sgr"45 is 1.41 times as large as "sgr"0.
This means that open angles (NA) of a beam that illuminates one spot on the reticle 10 differs in the directions of 0xc2x0 and 45xc2x0, which, in turn, means that a difference in resolving power occurs in relation to these two directions when a pattern on the reticle 10 is projected onto the wafer 12.
A "sgr" adjustment stop having, e.g., a circular aperture, when provided before the fly-eye lens 8xe2x80x2 plane of exit 8b would eliminate the foregoing anisotropy of "sgr". However, this requires so many "sgr" adjustment stops corresponding to the number of kinds of a settings, making the continuous "sgr" changing practically impossible.
Accordingly, it is an object of the present invention to provide an improved projection exposure apparatus having no the above "sgr" anisotropy.
In addition, it is a supplementary object to provide a projection exposure apparatus that miniaturizes an illumination system and improves the durability, without lowering luminous intensity, and without necessarily requiring a switching mechanism for the a adjustment stop at the side of fly-eye lens""s plane of exit.
In order to achieve the foregoing object, an illumination apparatus of one aspect of the present invention includes an inner-surface reflecting type integrator, an optical system for directing a beam from a light source to a portion of incidence of the inner-surface reflecting type integrator, an wave-front splitting type integrator, an image-forming optical system for arranging the portion of incidence of the inner-surface reflecting type integrator approximately conjugate with a portion of incidence of the wave-front splitting type integrator, and for directing a beam from the beam mixer to the wave-front splitting type integrator, and an irradiating optical system for superimposing multiple beams from the wave-front splitting type integrator on a plane to be irradiated, wherein a stop is provided at or near the portion of exit of the inner-surface reflecting type integrator.
The inner-surface reflecting type integrator may reflect at least a part of incident light with an internal surface of the inner-surface reflecting optical integrator, and for forming a surface light source on or near the plane of exit of the inner-surface reflecting optical integrator. The inner-surface reflecting type integrator may be a lens array for splitting a wave front of incident light, and for forming multiple secondary light sources on or near the portion of exit of the inner-surface reflecting type integrator.
The stop may be a mechanical aperture stop. Alternatively, the stop may be made of a light shielding material applied onto the portion of exit of the inner-surface reflecting type integrator, or made of a multi-layer film vapor-deposited onto the portion of exit of the inner-surface reflecting type integrator, or made of a metallic film vapor-deposited onto the portion of exit of the inner-surface reflecting type integrator.
In the foregoing illumination apparatus, the image-forming system may be a zoom optical system.
The portion of exit of the beam mixer may have a polygonal shape, and the stop may have an aperture for correcting "sgr" anisotropy. The stop has an approximately circular aperture. The stop has apertures having an approximately equal diameter at least in four directions of 0xc2x0, 45xc2x0, 90xc2x0, and 135xc2x0.
An illumination apparatus of another aspect of the present invention includes an inner-surface reflecting type integrator including a portion of exit with an n-gonal shape where n is a natural number, a wave-front splitting type integrator, a zoom optical system for projecting an image of the portion of exit of the inner-surface reflecting type integrator, onto a portion of incidence of the wave-front splitting type integrator, and an irradiating optical system for superimposing multiple beams from the wave-front splitting type integrator on a plane to be irradiated, wherein a stop having an approximately circular aperture is provided at or near the portion of exit of the inner-surface reflecting type integrator.
An illumination apparatus of still another aspect of the present invention includes an inner-surface reflecting type integrator including a portion of exit with a n-gonal shape where n is a natural number, a first condensing optical system for condensing a beam from a light source to a portion of incidence of the inner-surface reflecting type integrator, a wave-front splitting type integrator, a zoom optical system for projecting an image of the portion of exit of the inner-surface reflecting type integrator, onto a portion of incidence of the wave-front splitting type integrator, and a second condensing optical system for condensing a beam from an irradiating optical system for superimposing multiple beams from the wave-front splitting type integrator on a plane to be irradiated, wherein there is provided a stop having an aperture with an approximately 2n-gonal shape where n is a natural number at or near a portion of incidence of the inner-surface reflecting type integrator.
A projection exposure apparatus of still another aspect of the present invention includes any one of the above illumination apparatuses for illuminating a mask located on a plane to be illuminated, and a projection optical system for projecting a pattern on the mask onto a wafer. A device fabrication method of still another aspect of the present invention includes the steps of projecting a pattern on a mask onto a wafer by using one of the above projection exposure apparatuses, and developing the wafer to which the pattern was transferred.